In order to reduce the cutting resistance at the time of a cutting process, a thinning is generally provided at a tip end portion of a drill such as a twist drill that is disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-271811.
According to the twist drill, the length of a chisel edge can be shortened by providing a thinning 5, and a contact area with a workpiece can be accordingly reduced at the time of the cutting process, which results in reduction of the cutting resistance.
Further, according to the twist drill, a thinning edge 6 is formed by providing the thinning 5, so that the workpiece can be cut by the thinning edge 6 together with a cutting edge 3 at the time of the cutting process.